Coccidiosis, especially poultry coccidiosis, is a major problem in the poultry industry and if not controlled mortality and morbidity caused thereby effect serious economic loss in the raising of poultry.
Coccidiosis is a disease caused by a protozoa parasite of microscopic size called coccidia, belonging to the genus Eimeria. It is specific to the host animal. Thus, the finding that a coccidiostatic agent is suitable for use against one species of Eimeria in a host of a specific species does not necessarily carry with it the implication that it will be equally effective against other species of Eimeria in the same or other species of hosts. In fact, many coccidiostatic agents, while being effective against a specific species of Eimeria in a host animal, will not evidence this efficacy against other species of Eimeria in the same host animal.
Coccidiosis affects most animals raised commercially for food purposes, particularly poultry, such as turkeys, ducks, chickens and the like; sheep, cattle, swine, etc., are also affected. For example, in the poultry industry, no problems are more serious and more common than those resulting from parasitic diseases such as coccidiosis. The problem is especially great in this industry since the new techniques for raising poultry require that the birds be confined to narrow environs and, thus, be raised under crowded conditions. This close proximity of the birds while being raised is conducive to coccidiosis infections and the rapid spread thereof.
Infection is caused by the invasion of the animals by the protozoa parasite, coccidia. The infection in the host animals is initiated by the ingestion, usually along with feed or water, of Eimeria organisms in the sporulated oocyst stage. When the ingested oocysts enter the intestine, the infectious stage of the Eimeria soon develops from the oocysts and causes extensive damage to the inner walls of the intestine and the cecum or "intestinal pouch." There are both chronic and acute forms of coccidiosis infection in chickens. One type called cecal coccidiosis is caused primarily by the organism E. tenella and results in the destruction of the cecal linings of the host.
Intestinal coccidiosis in chickens results primarily from other species of Eimeria and is equally as serious from an economical point of view. Such species of Eimeria are exemplified by E. necatrix, E. acervulina, E. maxima, E. brunetti, E. hagani, E. praecox, E. mitis, etc. Other organisms, such as E. gallopavonis, E. meleagrimitis, E. adenoeides, E. meleagridis, E. dispersa, E. innocua, E. subrotunda, etc., cause coccidiosis infections in turkeys. In the duck and goose, E. truncata, E. anseris, etc.; in cattle, E. bovis, E. zurnii, E. alabamansis, E. auburnensis, etc.; in sheep, E. ashsata, E. parva, E. faurei, E. arloingi, etc.; in pigs, E. debliecki, E. spinosa, etc. cause coccidiosis. Thus, it is apparent from the above that the various species of Eimeria cause infection to a type specific to host animals.
In poultry, e.g., chickens and turkeys, in an outbreak of coccidiosis, the flock becomes seriously infected with little or no forewarning and a very high mortality can result unless the birds are promptly treated. Animals that do survive these types of infections are usually of lessened economical value inasmuch as they are quite inefficient in converting feed to weight gains, grow much more slowly than normal animals and frequently appear listless.
As is noted above, coccidiosis is, additionally, a disease problem in other larger animals such as lamb, sheep, calf, cattle and pigs, although of less concern than it is in the poultry industry. However, an awareness is currently developing in connection with the raising of these animals of the effect of coccidiosis thereon from an economical point of view, and the concerned people in the field are beginning to recognize that the problems resulting from an outbreak of coccidiosis should not be overlooked. In such an outbreak in larger animals, the herd also becomes seriously infected with little or no forewarning. It is readily apparent that even a low mortality rate in a herd of larger animals from coccidiosis has serious economic consequences due to the large loss incurred per animal unit.
A number of coccidiostatic agents are presently available for either the therapy or prevention of coccidiosis and some of these agents are effective in preventing high mortality among the infected animals. Still, outbreaks of coccidiosis among the animals occur due, in some cases, to the development of resistance of the Eimeria to known coccidiostats. Furthermore, animals treated with certain known coccidostats sometimes show a lower feed efficiency and less rapid weight gains than healthy animals. Moreover, many of the known coccidiostats have been found to possess a limited anticoccidial species spectrum and they are also often too expensive for wide use such as in poultry husbandry, particularly in view of the high concentration levels at which they must be used in order to achieve the desired end.
Therefore, a definite need exists for an antiparasitic composition which is effective in the treatment and control of coccidiosis caused by a broad spectrum of Eimeria organisms in animals but which does not suffer from the defect of lowering the feed efficiency and growth. Furthermore, greatly desired from the animal raisers point of view, is a highly effective coccidiostat which is well tolerated by the host.